A lost wax casting process can be used to produce casting molds for various products. The lost wax process includes forming a casting pattern of the desired finished product and surrounding the casting pattern with liquid investment during an investment phase. Typically, the casting pattern is made of wax or other such material. When the investment hardens, the casting pattern is eliminated (e.g., burned out) from the hardened investment during an elimination phase to provide a pattern cavity shaped like the casting pattern. Liquid and/or vapor solvents can also be used to remove the casting pattern. Material, such as molten metal or pressable ceramic, can be directed (e.g., poured or pressed) into the pattern cavity during a casting phase and allowed to cool in order to cast the desired product. The hardened investment is then destroyed to recover the casting.
To provide a path (i.e., a sprue) through the investment to the pattern cavity, a sprue former can be invested along with the casting pattern. The sprue former generally extends from the casting pattern to the exterior of the investment. Typically, the sprue former is made of the same material as the casting pattern and is eliminated along with the casting pattern during the elimination phase. The resulting sprue directs the casting material through the hardened investment to the pattern cavity during the casting phase. After the casting material hardens, excess material hardened in the sprue is removed from the casting.
To produce dental prostheses (e.g., dental copings, dental crowns, etc.) using the process described above, technicians obtain electronic models of dentitions of patients. The technicians can design electronic models of dental prostheses based on the electronic models of the dentitions. In some prior systems, the technicians obtain impressions and/or plaster models of the dentitions from dentists or other dental/orthodontic professionals. The impressions and/or models can be scanned to produce electronic models of the dentitions. In other prior systems, electronic images can be obtained by directly scanning the mouths of the patients. Rapid prototyping (i.e., automated prototyping) techniques can print casting patterns based on the prostheses models. Such casting patterns can be used in forming casting molds using the lost wax process described above. The prostheses can be cast from metal, ceramic, or a combination of the two using the casting molds.
As dental prostheses tend to be small, multiple prostheses are typically cast simultaneously. This simultaneous casting is accomplished using a multi-piece sprue former. A multi-piece sprue former is a structure designed to leave a series of interconnected channels or passageways within the hardened investment connecting each of the pattern cavities to the exterior of the investment. Molten casting material can be poured into the series of sprues and thereby directed to each pattern cavity.
There exists a need in the art for improved sprue formers.